## Chapter Objectives and Summaries

### CHAPTER 14 Wave motion in two dimensions.

LEARNING OBJECTIVES
Knowledge of subject matter
• Explain the meaning of the following terms: speed of wave, frequency, wavelength, amplitude, period, pulse, node, anti-node, standing wave, phase.
• Describe the diffraction of water waves through single slits of different widths and around obstacles.
• Describe the reflection and refraction of waves in water
• State the meaning of the terms;(a) direction of propagation.(b) angle of incidence.(c) angle of reflection.(d) angle of refraction.
• Describe the diffraction of waves through a slit and around a barrier
• Recognise wave motion as a means of energy transfer.
• Solve simple problems involving reflection, refraction, diffraction and interference of water waves (n1 sin ø1 = n2 sin ø2 or n1v1 = n2v2).

SCIENTIFIC PROCESSES

• Predict direction of reflected and/or refracted wave from given incident wave from wave patterns in water
• Diagramatcally show the wave pattern produced by interfering waves
• Identify nodal and anti-nodal lines on an interference pattern
• Analyse relevant graphs.(a) displacement v time.(b) distance v time associated with wave motion.
• Investigate standing waves patterns in water
• Draw diagrams to show reflection of waves in water from straight and curved boundaries
• Infer the interference pattern of water waves from sources in phase
• Draw and explain interference patterns formed from two point sources.

COMPLEX REASONING PROCESSES

• Solve complex problems on diffraction, interference, reflection and refraction.
• Predict outcomes of wave interactions.

### CHAPTER 14 SUMMARY

• Wavefronts produced by disturbances in a medium move away from the source. The direction of propagation of the wave will be perpendicular to the wavefront.
• Waves can be reflected, refracted, and, diffracted as well as interfere with each other.
• When waves reflect off a barrier the angle of incidence equals the angle of reflection.
• Refraction is the change in direction of a wave when it passes from one medium to another.
• When a wave travels from one medium to another its velocity and wavelength changes but its frequency remains the same.
• Diffraction is the bending of waves as they pass through a slit or around objects.
• Diffraction is most noticeable when the size of the aperture is less than or comparable to the wavelength of the wave.
• Interference is the interaction of waves produced from two sources. When this occurs an interference pattern is produced and is characterised by nodal and antinodal lines.
• Nodal lines are the lines produced when nodal points, points of destructive interference, are connected.
• Antinodal lines are the lines produced when antinodal points, points of constructive interference, are connected.
• The path difference of all points on the same antinodal line is the same. The path difference of points on the `nth' antinodal line is equal to n.l. Where n = 1,2,3..
• The path difference of all points on the same nodal line is the same. The path difference of points on the `nth' nodal line is equal to (n - ½).l. Where n = 1,2,3..